Stretch-Shortening Cycle in Human Muscle Contraction: The Role of the Stretch Reflex in Force Production in Various Vertical Jumps

179 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.Although researchers agree that both the stretch reflex and the elasticity of the muscle contribute to the effectiveness and efficiency of human performances, the relative contributions of each have not been determined, because no direct measurements have been utilized. Therefore, the purpose of this study was to investigate the stretch reflex contribution during vertical jumping performance and to determine the ratio of the stretch reflex contribution relative to elasticity in the stretch-shortening contraction of the vastus lateralis muscle during the following vertical jumps: counter-movement jump (CMJ), counter-movement hop (CMH), drop jump (DJ), squatting jump tense (SJT), squatting jump rested (SJR), and squatting jump hop (SJH). The vastus lateralis muscle of eight male athletes (18-33 years of age) was injected with NOVOCAIN, 4-10cc solution of 1% concentration. A validation of the stretch reflex blockage was determined by a series of patellar tendon reflex tests. Integrated EMG (IEMG) activity of the vastus lateralis muscle and ground reaction forces via an AMTI force platform were recorded during the six jumps performed pre- and post-injection. High-speed cinematography and videography were used to obtain optical data of the jumping performances. Repeated measure ANOVA was used to analyze the data on different number of subject groups in this study and p value of.05 and better was selected for the significance level. The following variables, jump height, maximum force, vertical velocity, IEMG Impulses and power were measured. There was a significant reduction of the height in the average of the two subjects group (15%), IEMG (20%), vertical velocity (7%), and power (9.5%) for the CMH after stretch reflex block. The height in the SJH (7%) and the DJ (10%) were also reduced significantly. No changes occurred in the SJT and SJR since there was no fast stretching phase in these conditions. It was concluded that the contribution of the stretch reflex is variable and greatly dependent upon both the type of jump and the individual performer. Finally, it was evident that the stretch reflex contributes to the CMH height by at least 75% of force enhancement.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD